In many multi-speed transmissions it is desirable to engage only certain clutches in a particular sequence in order to eliminate sudden changes of the force level on the components of the transmission. For example, it is detrimental to the transmission components if the forward clutch and the reverse clutch both became engaged while the vehicle is moving in one direction or the other. Furthermore, in a transmission having several speeds, it is detrimental to the transmission components to have the transmission shift from one of the highest speeds to one of the lowest speeds without going through the intermediate speeds.
In some automatic transmissions a control system is provided which senses operating control pressure and inhibits the transmission from downshifting if the vehicle speed is too fast. Even though this type of control is workable; it is a complicated system requiring several extra components and is restricted for use on automatic transmissions.
In other systems utilizing several clutches, the control valves are independently arranged in the control valve housing and independently actuated in response to movement of a speed or directional control lever. In these arrangements there is a possibility that more than one speed clutch could be engaged at one time. Furthermore, in this type of system, the control valves are relying on the force of a spring to move the valving element to the disengaged position.
In systems having forward and reverse clutches, several arrangements have been provided to ensure that only one of the forward and reverse clutches may be actuated at one time. In these systems, both valving elements are normally physically located in the same bore in such a manner that if one of the valving elements is in an actuated position the other one is physically prohibited from moving to an actuated position. In these systems the valving elements are normally moved to their actuated positions by pressurized fluid and retracted by spring force. These are effective in allowing only one of two clutches to engage at one time but are limited in that both valving elements must be in a common bore and each must rely on spring forces for moving the valving element in one direction of travel.
The present invention is directed to overcoming one or more of the problems as set forth above.